The crown, or portion of the tooth exposed from the gums, is completely encased in a layer of enamel, which provides the tooth with its hardness and structure. The main component of the complex crystalline lattice forming the material is a calcium phosphate mineral called hydroxyapatite. Saliva has a specific pH allowing for a natural occurrence of demineralization and remineralization, which adds and removes some of the minerals housed in the exposed enamel. This process is usually held in equilibrium under normal physiological conditions. However, some situations can steer the process towards a greater amount of demineralization than remineralization. Demineralization is caused by a drop in pH in the mouth lower than 5.6, which can result from an increase in organic acid produced by oral microorganisms that form a biofilm on the tooth's enamel. Such microorganisms are capable of consuming sugars and carbohydrates left in the mouth after food is consumed and produce acids which lower the pH at the surface of the tooth. This low pH causes demineralization to take over, and more minerals leech from the tooth surface. If left unchecked, weakened enamel, decay, and cavities can form.
Fluoride reacts with hydroxyapatite to form a strong compound that is less prone to acidic attacks. Fluoride has also been shown to remineralize damaged enamel in the early stages of demineralization, as well as prevent further bacteria growth. The biofilm accumulated on the tooth surface is generally removed by good oral hygiene including brushing the teeth with a fluoride-containing toothpaste, flossing, and rising with mouthwash.
Patients with fixed orthodontic braces confront the challenge of attempting to clean the tooth surfaces close to the brace bracket that a toothbrush cannot reach. Poor cleaning close to the bracket can form a biofilm, which in some cases can result in increased decay and white-spot lesioning.